Being successful isn't always about having talent. Often, it's hard work that really pays off.

That's according to legendary New England Patriots coach Bill Belichick, who helped Tom Brady become one of the most successful quarterbacks of all time and is leading the team to Super Bowl on Sunday for its potential sixth win.

Belichick sat with CNBC contributor Suzy Welch for a rare interview in 2017 to talk about his leadership tips and historic career.

During the conversation, Belichick admitted that Brady wasn't blessed with overwhelming athletic skill. Rather, it's been learned. "He's not a great natural athlete, but he's a very smart, instinctive football player," he told Welch.

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Brady happens to agree, acknowledging he has always felt more mentally equipped for the game than physically equipped, as he detailed in his 2017 book "The TB12 Method: How to achieve a lifetime of sustained peak performance."

One of Brady's biggest priorities over the past decade has been making sure he has the right mental toughness and attitude.

"When you're in a Super Bowl game and your team is three touchdowns down and the clock is running, mental toughness is what makes the difference at the end," he wrote.

In Belichick's interview with Welch, the Patriots coach said Brady has three traits that have turned him into one of the NFL's all-time greats.

1. He has a strong work ethic

Belichick is quick to praise Brady, whom he's coached since 2000, on his ability to put in the time to get better and win. "Tom works very hard," he said. "He wasn't all that good when we got him. He mechanically wasn't anywhere near where it eventually has ended up."

Over the years, though, that's changed. "Nobody's worked harder than Tom. He's trained hard. He's worked hard on his throwing mechanics. He's earned everything that he's achieved," Belichick said.

"It wasn't always there," he added.

2. He thinks strategically

Coupled with his ability to constantly improve athletically, Brady also has a mind for strategy. "On the field he sees things," Belichick said. "He's got a great ability to take and [process] a large amount of information very quickly."

"He has great football vision, awareness, and understanding, again, of what we do and what our opponents do," he said.

3. He stays in the moment

The third trait that Brady embodies is being able to live in the present. "He can really focus on short-term goals," Belichick said.

"He can focus on just this week, and then as soon as this week's over, totally put it out [of mind] and go to next week when the challenges are completely different."